Solved Windows 8.1 and Windows 10

[Clint]

Can you have Windows 8.1 running and Windows 10 (not preview) running on virtual machine at the same time with the same key?

 

[Brink]

Hello Clint,

Sorry, but no. It would violate the EULA since those would be considered two separate installations, and could get them both deactivated.

 

[Clint]

Thanks Brink. If I upgrade to 10 and it's activated and I don't like it. Can I go back to 8.1 and will it activate again?

 

[Brink]

Yes. You won't have any issues doing that.

In fact, Microsoft has made it easy to go back to your previous Windows if you do so within 30 days of upgrading to Windows 10.

Windows 10 - Go Back to Previous Windows - Windows 10 Forums

 

[Steve C]

I've been running Windows 10 on virtual machine for a while without activating it. You can't personalise it but the unactivated version is fine for trying out Windows 10 and checking your software & drivers work.